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  26 <div class="refentry">
  27 <a name="boost.type_erasure.param"></a><div class="titlepage"></div>
  28 <div class="refnamediv">
  29 <h2><span class="refentrytitle">Class template param</span></h2>
  30 <p>boost::type_erasure::param &#8212; A wrapper to help with overload resolution for functions operating on an <a class="link" href="any.html" title="Class template any">any</a>. </p>
  31 </div>
  32 <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
  33 <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../boost_typeerasure/reference.html#header.boost.type_erasure.concept_of_hpp" title="Header &lt;boost/type_erasure/concept_of.hpp&gt;">boost/type_erasure/concept_of.hpp</a>&gt;
  34
  35 </span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Concept<span class="special">,</span> <span class="keyword">typename</span> T<span class="special">&gt;</span>
  36 <span class="keyword">class</span> <a class="link" href="param.html" title="Class template param">param</a> <span class="special">{</span>
  37 <span class="keyword">public</span><span class="special">:</span>
  38   <span class="comment">// <a class="link" href="param.html#boost.type_erasure.paramconstruct-copy-destruct">construct/copy/destruct</a></span>
  39   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> U<span class="special">&gt;</span> <a class="link" href="param.html#idp758757792-bb"><span class="identifier">param</span></a><span class="special">(</span><a class="link" href="../any.html" title="Class any">any</a><span class="special">&lt;</span> <span class="identifier">Concept</span><span class="special">,</span> <span class="identifier">U</span> <span class="special">&gt;</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  40   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> U<span class="special">&gt;</span> <a class="link" href="param.html#idp758759904-bb"><span class="identifier">param</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="../any.html" title="Class any">any</a><span class="special">&lt;</span> <span class="identifier">Concept</span><span class="special">,</span> <span class="identifier">U</span> <span class="special">&gt;</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
  41   <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> U<span class="special">&gt;</span> <a class="link" href="param.html#idp758762176-bb"><span class="identifier">param</span></a><span class="special">(</span><a class="link" href="../any.html" title="Class any">any</a><span class="special">&lt;</span> <span class="identifier">Concept</span><span class="special">,</span> <span class="identifier">U</span> <span class="special">&gt;</span> <span class="special">&amp;&amp;</span><span class="special">)</span><span class="special">;</span>
  42
  43   <span class="comment">// <a class="link" href="param.html#idp758754512-bb">public member functions</a></span>
  44   <a class="link" href="../any.html" title="Class any">any</a><span class="special">&lt;</span> <span class="identifier">Concept</span><span class="special">,</span> <span class="identifier">T</span> <span class="special">&gt;</span> <a class="link" href="param.html#idp758755072-bb"><span class="identifier">get</span></a><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span>
  45 <span class="special">}</span><span class="special">;</span></pre></div>
  46 <div class="refsect1">
  47 <a name="idp565856176"></a><h2>Description</h2>
  48 <p>The template arguments are interpreted in the same way as <a class="link" href="any.html" title="Class template any">any</a>.</p>
  49 <p>A parameter of type <a class="link" href="param.html" title="Class template param">param</a> can be initialized with an <a class="link" href="any.html" title="Class template any">any</a> that has the same <code class="computeroutput">Concept</code> and base placeholder when there exists a corresponding standard conversion for the placeholder. A conversion sequence from any&lt;C, P&gt; to param&lt;C, P1&gt; is a better conversion sequence than any&lt;C, P&gt; to param&lt;C, P2&gt; iff the corresponding placeholder standard conversion sequence from P to P1 is a better conversion sequence than P to P2.</p>
  50 <div class="note"><table border="0" summary="Note">
  51 <tr>
  52 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../doc/src/images/note.png"></td>
  53 <th align="left">Note</th>
  54 </tr>
  55 <tr><td align="left" valign="top"><p>Overloading based on cv-qualifiers and rvalue-ness is only supported in C++11. In C++03, all conversion sequences from <a class="link" href="any.html" title="Class template any">any</a> to <a class="link" href="param.html" title="Class template param">param</a> have the same rank.</p></td></tr>
  56 </table></div>
  57 <p>
  58 Example:</p>
  59 <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">f</span><span class="special">(</span><span class="identifier">param</span><span class="special">&lt;</span><span class="identifier">C</span><span class="special">,</span> <span class="identifier">_a</span><span class="special">&amp;</span><span class="special">&gt;</span><span class="special">)</span><span class="special">;</span>
  60 <span class="keyword">void</span> <span class="identifier">f</span><span class="special">(</span><span class="identifier">param</span><span class="special">&lt;</span><span class="identifier">C</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">_a</span><span class="special">&amp;</span><span class="special">&gt;</span><span class="special">)</span><span class="special">;</span>
  61 <span class="keyword">void</span> <span class="identifier">g</span><span class="special">(</span><span class="identifier">param</span><span class="special">&lt;</span><span class="identifier">C</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">_a</span><span class="special">&amp;</span><span class="special">&gt;</span><span class="special">)</span><span class="special">;</span>
  62 <span class="keyword">void</span> <span class="identifier">g</span><span class="special">(</span><span class="identifier">param</span><span class="special">&lt;</span><span class="identifier">C</span><span class="special">,</span> <span class="identifier">_a</span><span class="special">&amp;&amp;</span><span class="special">&gt;</span><span class="special">)</span><span class="special">;</span>
  63
  64 <span class="identifier">any</span><span class="special">&lt;</span><span class="identifier">C</span><span class="special">,</span> <span class="identifier">_a</span><span class="special">&gt;</span> <span class="identifier">a</span><span class="special">;</span>
  65 <span class="identifier">f</span><span class="special">(</span><span class="identifier">any</span><span class="special">&lt;</span><span class="identifier">C</span><span class="special">,</span> <span class="identifier">_a</span><span class="special">&gt;</span><span class="special">(</span><span class="special">)</span><span class="special">)</span><span class="special">;</span> <span class="comment">// calls void f(param&lt;C, const _a&amp;&gt;);</span>
  66 <span class="identifier">f</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span><span class="special">;</span>            <span class="comment">// calls void f(param&lt;C, _a&amp;&gt;); (ambiguous in C++03)</span>
  67 <span class="identifier">g</span><span class="special">(</span><span class="identifier">any</span><span class="special">&lt;</span><span class="identifier">C</span><span class="special">,</span> <span class="identifier">_a</span><span class="special">&gt;</span><span class="special">(</span><span class="special">)</span><span class="special">)</span><span class="special">;</span> <span class="comment">// calls void g(param&lt;C, _a&amp;&amp;&gt;); (ambiguous in C++03)</span>
  68 <span class="identifier">g</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span><span class="special">;</span>            <span class="comment">// calls void g(param&lt;C, const _a&amp;&gt;);</span>
  69 </pre>
  70 <p> </p>
  71 <div class="refsect2">
  72 <a name="idp565919744"></a><h3>
  73 <a name="boost.type_erasure.paramconstruct-copy-destruct"></a><code class="computeroutput">param</code>
  74         public
  75        construct/copy/destruct</h3>
  76 <div class="orderedlist"><ol class="orderedlist" type="1">
  77 <li class="listitem"><pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> U<span class="special">&gt;</span> <a name="idp758757792-bb"></a><span class="identifier">param</span><span class="special">(</span><a class="link" href="../any.html" title="Class any">any</a><span class="special">&lt;</span> <span class="identifier">Concept</span><span class="special">,</span> <span class="identifier">U</span> <span class="special">&gt;</span> <span class="special">&amp;</span> a<span class="special">)</span><span class="special">;</span></pre></li>
  78 <li class="listitem"><pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> U<span class="special">&gt;</span> <a name="idp758759904-bb"></a><span class="identifier">param</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="../any.html" title="Class any">any</a><span class="special">&lt;</span> <span class="identifier">Concept</span><span class="special">,</span> <span class="identifier">U</span> <span class="special">&gt;</span> <span class="special">&amp;</span> a<span class="special">)</span><span class="special">;</span></pre></li>
  79 <li class="listitem"><pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> U<span class="special">&gt;</span> <a name="idp758762176-bb"></a><span class="identifier">param</span><span class="special">(</span><a class="link" href="../any.html" title="Class any">any</a><span class="special">&lt;</span> <span class="identifier">Concept</span><span class="special">,</span> <span class="identifier">U</span> <span class="special">&gt;</span> <span class="special">&amp;&amp;</span> a<span class="special">)</span><span class="special">;</span></pre></li>
  80 </ol></div>
  81 </div>
  82 <div class="refsect2">
  83 <a name="idp565954784"></a><h3>
  84 <a name="idp758754512-bb"></a><code class="computeroutput">param</code> public member functions</h3>
  85 <div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
  86 <pre class="literallayout"><a class="link" href="../any.html" title="Class any">any</a><span class="special">&lt;</span> <span class="identifier">Concept</span><span class="special">,</span> <span class="identifier">T</span> <span class="special">&gt;</span> <a name="idp758755072-bb"></a><span class="identifier">get</span><span class="special">(</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre>
  87 <p>Returns the stored <code class="computeroutput"><a class="link" href="any.html" title="Class template any">any</a></code>. </p>
  88 </li></ol></div>
  89 </div>
  90 </div>
  91 </div>
  92 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
  93 <td align="left"></td>
  94 <td align="right"><div class="copyright-footer">Copyright &#169; 2011-2013 Steven Watanabe<p>
  95         Distributed under the Boost Software License, Version 1.0. (See accompanying
  96         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
  97       </p>
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